Funds are requested to upgrade the Duke SPECT Research Instrument. The overall goal is to enhance research progress of Instrument Users supported by the National Institutes of Health, and other federal agencies, by providing a high performance, reliable and quantitative SPECT Research Instrument The Duke SPECT Research Instrument was originally acquired in 1988, primarily with support from the NIH BRS Shared Instrumentation Grant Program. The SPECT Research Instrument has been used as a research instrument for the past 13 years for in vivo and vitro studies. Over this period Duke investigators have designed and built several unique research grade collimators and specialized phantom- positioning assemblies that can be used with the SPECT Research Instrument. The in-house developed research collimators include: a) an ultra-high resolution rotating parallel hole collimator for imaging therapeutic doses of I-131-labeled monoclonal antibodies (MAbs); b) symmetric and asymmetric half fan beam collimators for acquiring transmission data to determine SPECT attenuation maps; 3) symmetric and asymmetric half cone beam collimators for brain and breast imaging; and d) ultra-high resolution pinhole collimators for small animal imaging, and ultra-high resolution imaging of therapeutic doses of I-131- labeled MABS. These accessories are important and unique research resources for the User Group. Their design and construction required a significant investment in time, effort and financial support. The current SPECT Research Instrument has performed for many years, has served many of the Users' needs, and advanced their research progress. Presently the Instrument is aging and becoming increasingly difficult to maintain, and there are a few instrinsic characteristics that limit its overall effectiveness as a research instrument for some Users' applications. For example, retraction of the heads is limited to only 27 cm, thereby the field of view for transmission data acquisition is markedly reduced. An important objective of this proposal is to ensure that the custom research collimators and specialized assemblies remain compatible and functional with the newly upgraded SPECT Instrument. A second objective is to improve upon the present system's intrinsic performance characteristics. Both of these objectives can be successfully attained by replacing the triple head SPECT Instrument with a current generation triple head SPECT Instrument. This essential SPECT Laboratory upgrade will ensure that the Users continue to have a dedicated and highly quantitative SPECT instrument available that will enhance their research progress, help them to accomplish their long term research goals, and allow them to investigate new techniques and approaches to quantitative imaging.